by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

FEP Encapsulated O-Rings

FEP encapsulated o-rings can survive corrosive chemicals and retain their sealing power in extreme temperatures, which is the main reason more and more engineers are choosing them for harsh environment applications. But what makes these particular o-rings special and what options are available for them?

What Makes Encapsulated O-Rings Different?

Unlike traditional o-rings, encapsulated o-rings contain a solid or hollow core that is typically made from a very elastomeric material. The exterior of the encapsulated o-ring is able to protect the encased elastomer from corrosive media that would adversely affect its performance. Together, the core and encapsulating polymer are able to provide a highly reliable seal even in extremely harsh conditions that may involve aggressive chemicals, extreme temperatures, and high pressures.

Encapsulated o-rings can be used in a wide variety of applications, including flanges, swivels, joints, valve stems, pumps, and even rocket engines. They serve as an excellent replacement for solid PTFE o-rings that are just not flexible enough for sealing in the long term. 

Characteristics of FEP

One of the most popular materials for the jacket of an encapsulated o-ring is FEP (fluorinated ethylene propylene), which has several trade names including Teflon FEP, Neoflon FEP, and Dyneon FEP. It is well known for its resistance to chemical attack, low friction, and a wide operating temperature range of -420°F through 400°F.  FEP remains flexible even at cryogenic temperatures, as well. One of its key characteristics is a very low compression set, allowing it to return to its original shape after deformation. FEP is also non-flammable and easy to lubricate.

While FEP is often compared to PTFE (Teflon), there are several key differences to keep in mind. For example, it does have a low coefficient of friction but it is higher than PTFE; at the same time, it still possesses very low friction with minimal stick-slip behavior. In addition, FEP does exhibit better vapor and gas permeability, which could be key for some applications. It is also melt processable, which means it can be vacuum formed, injection molded, and extruded. And, like PTFE, it is easy to clean even viscous liquids from.

FEP is available in FDA-approved grades, is considered a high purity material, and is less expensive than PFA, another commonly used jacket material. Note that FEP is commonly used in applications such as pump housings, medical components, food processing, fluid handling, and chemical processing.

Recommended Cores for FEP

FEP encapsulated o-rings work especially well with FKM and silicone cores, but there are other options available. FKM, which is a fluro-elastomer, has rubber-elastic properties which allow it to reassume its original shape and form after deformation. This results in excellent properties related to compression set. Silicone cores are not as stiff or hard as FKM cores and exhibit very good flexibility, even in cold temperatures. When combined with a hollow core geometry, this additional flexibility means that less energy is needed to achieve a tight seal. They work best for applications that involve low compressive forces.

Cores made from stainless steel, such as SS 301 or 302, exhibit excellent performance at both cryogenic and high temperatures, ranging from -420°F to 500°F. These cores usually take the form of a spiral spring (not unlike spring-energized seals) and exhibit minimum compression set and good resilience. They are not commonly used with FEP, however. EPDM, which stands for ethylene propylene diene monomer, is a synthetic rubber that performs well in temperatures ranging from -58°F to 300°F. Again, this particular core material is not recommended for use with FEP.

Selecting an FEP Encapsulated O-Ring

First, there are limitations associated with FEP encapsulated o-rings. They should not be used with liquid alkali metals and some fluorine  compounds, and should not be exposed to abrasive media such as slurries and some powders. 

They are not suitable for applications that involve high pressures and are limited to static or slow moving applications. In addition, they are not recommended for applications where the o-ring will be highly elongated and end-users should be aware that installation forces will be higher for FEP encapsulated o-rings.

However, experts agree that chemical attack and swelling are among the most common causes of o-ring failure, and the use of FEP encapsulated o-rings can solve both of these issues. FEP with an FKM core is a standard solution with a low compression set, recommended for operating temperature ranges not exceeding -4°F to 401°F. 

Use of a solid silicone core results in better low temperature performance, with an operating temperature range of -46°F to 401°F. A hollow core, on the other hand, involves lower contact pressures and is ideal for sensitive or fragile equipment. 

Conclusion

FEP encapsulated o-rings involve several key advantages, starting with their excellent chemical resistance, which allows them to be used with corrosive chemicals. These o-rings can handle pressures up to 3,000 psi and provide both an excellent service life and reliable sealing, all at a cost effective price. Their reliability and durability also translate to less downtime and better M&O costs. If corrosive media or extreme temperatures are destroying your o-rings, it may be time to consider an FEP encapsulated solution.

Advanced-EMC will work with you to find the encapsulated o-ring solution your application needs, from FDA-approved solutions for use with food processing equipment or a reliable, cryogenically compatible solution for a rocket. Contact us today to learn more.

by Jackie Johnson Jackie Johnson No Comments

All About Thermoplastics

Thermoplastic elastomers, also known as thermoplastic rubbers, or simply TPEs, are some of the best materials for when your product needs to have more flexibility. In this week’s blog post, we will go over the different types of thermoplastics, a brief history, and the benefits compared to other materials.

Different Types of Thermoplastics

According to ISO 18064, commercial TPEs come in six different classes, each with slightly different properties that make it suited for certain tasks and applications.

Styrenic block copolymers, TPS (TPE-s)

TPS are tri-block copolymers containing an elastomeric midblock and a polystyrene endblock. They are non-toxic, odorless and resistant to many different chemicals and conditions. This makes them highly suitable to outdoor conditions.

Thermoplastic polyolefinelastomers, TPO (TPE-o)

TPOs are based on a polyethylene backbone. They offer low-density and high flexibility and are commonly used as additives to PE and PP compounds to make them more flexible.

Thermoplastic Vulcanizates, TPV (TPE-v or TPV)

TPVs are produced by dynamic vulcanization or cross-linking of a rubber during blending and melt-processing with a thermoplastic at elevated temperature. TPVs are inexpensive and can be produced in high-volume, making them a good alternative to cheaper elastomers.

Thermoplastic polyurethanes, TPU (TPU)

TPUs are a linear segmented block copolymer composed of both hard and soft segments. TPUs, like other elastomers, are flexible, but also offer additional sturdiness, high resilience and a good compression set, making the incredibly versatile.

Thermoplastic copolyester, TPC (TPE-E)

TPCs combine the flexibility and strength of thermoset rubber with the processing ease of engineered plastics. They are high performance and high temperature elastomers suitable for extreme conditions.

Thermoplastic polyamides, TPA (TPE-A)

TPAs are light-weight thermoplastic elastomers based on polyester-amide (PEA), polyether-esteramide (PEEA), or polyether-amide (PEBA) block copolymers. They have incredibly low temperature flexibility, making them suited for chemical environments.

Not classified thermoplastic elastomers, TPZ

TPZs are thermoplastic elastomers that do not fall in any of the above categories.

History of Thermoplastics

While the origins of TPEs date back to the 30s with the invention of poly vinyl chloride by DuPont, TPEs became readily available with the advent of thermoplastic polyurethane polymers in the 1950s.

The 1960s saw styrene block copolymer become available, and by the 1970s there were a ride range of TPE materials available commercially.

Benefits of Thermoplastics

TPEs have many benefits compared to other materials such as PTFE or silicone.

  • More Eco-Friendly than PTFE
  • More Cost Effective than Silicone
  • Consistent
  • Medical and Food Safe
  • Incredibly Versatile compared to other materials

If you need a material that is flexible, versatile, cost effective and eco-friendly, consider using thermoplastic elastomers!

If you need TPE seals, bearings or other industrial solutions, contact us at Advanced EMC Technologies today!